Then you need to study the quantum world
And I predict that the answers you find will spawn an equal number of questions. The root causes of mass, electromagnetism, gravity, strong and weak forces, spin, etc. seems to trace back (so far) to the quarks that compose matter. I don't think that the jury is in yet, so you may have to wait a few decades or centuries for satisfaction.
Or if you haven't the patience, you can skip all that messy experimental evidence and derive all the answers for yourself here at HZ.